Interior contour for bore of a friction support bearing of a railway locomotive traction motor

ABSTRACT

A contour or profile of a bore of a locomotive traction-motor support bearing structure, where such profile preserves the currently center-loading of the upper load zone but moves inboardly the lower load zone to a more general central location. The profile of the bore for the support bearing, according to the invention, takes into account not only truck-axle bending due to locomotive weight, but also that from motor tilt through bearing clearances, and couple action on the axle from heavy radial loads on PE support bearing and adjacent axle gear. The bore is configured such that the upper surface is horizontal, but the lower surface slopes downwardly in the outboard direction at an angle based on a function dependent upon the three misalignment factors. In a preferred embodiment, the bore mid-section is defined as a frustroconical section of a cone with an altitude having a slope of substantially 1×M 1  to the horizontal, and an apex angle of substantially arc tan 2×M 1 , where M 1  is the value of the misalignment factor associated with the locomotive load on the axle.

BACKGROUND OF THE INVENTION

The present invention is directed to a railway locomotive traction motorand, in particular, to the friction support bearing by which thetraction motor is partially supported on the axle of the railway truckmounting the underside of the locomotive, and, in particular, to amethod of customizing the geometry or bore-profile of a traction motorsupport-bearing bore in order to optimize alignment with the locomotiveaxle journal under heavy load conditions, and to thus increase bearingload capacity and bearing life under heavy load conditions.

Proper alignment between the support bearing and the truck axle journalis important for maintaining good bearing performance, because itprovides maximum contact between journal and bearing to thus insureminimum unit loading (lbs/sq.in.). This allows the bearing to carryheavier radial loads or the same radial load with greater reliability.This applies to both pinion end (PE) and commutator end (CE) bearings,although it is not as important at the CE position because of the lightradial loading at this location.

It is, also, common practice to use the same type of support bearing forboth the pinion end and commutator end. Thus, since the greater radialload occurs at the pinion end, such a support bearing must be sodesigned so as to withstand the greater wear at the pinion end. Thiscurrent parts-interchangeability requirement of support bearings for useat either pinion end or commutator end, therefore, results in a bearingwhich is acceptable for either position, but optimum for neitherposition. Therefore, it is current practice to use identical supportbearings at both the heavily loaded PE position and the lesser-loaded CEposition for locomotive traction motors equipped with plain frictionbearings. Thus, when providing a new type of bore for a support bearingfor a locomotive truck axle, ideally one would optimize the bearing borefor the misalignment conditions existing at the PE position, and do thisin a way which allows continued use at the CE position, even though notoptimized for that lesser-loaded bearing position.

The primary cause of support bearing misalignment is bending due tolocomotive weight, and this factor alone theoretically should tend tocause the upper load zone of the support bearing to move an in inboarddirection away from the center position of the support-bearing bore,while also causing the lower load zone thereof to move to an outboardlocation away from the center position of bore. However, in actual use,it has been found that such does not actually occur at the PE; instead,it has been found that upper load zone remains generallycentrally-located while the lower load zone does move off-center towardthe outboard end of the support bearing. The problem has been tounderstand why this occurs, and then to develop a bore-contour orprofile consistent with the findings as to the additional bendingtorques present causing the shift of the load zones from the expected,which contour will preserve the existing ideal location of the upperload zone while moving the lower zone into a central position.

In U.S. Pat. No. 4,940,002, which is incorporated by reference herein,there is disclosed a friction support bearing having, in a firstversion, a skewed or tilted internal bore design, which bore design moreaccurately positions the truck axle journal therein during heavy loadconditions. This prior-art bore design takes into consideration thetorque and bending loads of the truck axle arising from thelaterally-spaced radial forces emanating from the weight of thelocomotive acting on the journal box bearings at the end of the axle andthe reactive force of the rail track acting on the wheel mounted by theaxle, which bending of the axle directly causes misalignment of the axleportion extending through the traction-motor friction support bearingwith the bore of the support bearing. This misalignment causes excessiveloading and wear of the support bearing on the pinion-end thereofadjacent the axle's drive gear. However, while this prior-artbore-design may help to alleviate some excessive load concentration onthe pinion-end of the support bearing, it has not completely solved theproblem. In a second version U.S. Pat. No. 4,940,002, there is disclosedforming the interior bore as variable or changing conical sections,where there are actually four separate conical sections employed. Inthis second version, there is provided an upper central portion of thebore that is a substantially horizontal line or surface, when viewed invertical cross section, while the lower or bottom central portion of thebore is somewhat sloped.

The loading of a typical, prior-art traction-motor pinion-end supportbearing having a standard cylindrical bore without the improvedbore-profile of above-mentioned U.S. Pat. No. 4,940,002, is shown inFIG. 1. For best overall performance and life of a traction-motorsupport bearing 10, the load zones for loading the truck axle should becentered. This is so in order that the lubricant entering the interiorof the bearing via a wick window 12 lubricates all contactingsurface-areas, which wick lubricator contacts the axle's journal throughthe window. In addition, both load zones should be contained within thetotal axial dimension of the wick if at all possible, again to ensurethe best possible lubrication. The example shown in of FIG. 1 is forplain friction support bearings from traction motors with 8″ nominaldiameter axles, with approximately 60,000 to 70,000 pounds axle load andstandard gauge wheel spacing. This combination of parameters has an axlebending slope of about 0.001 inch/inch at the mid-length portion of thePE bearing. Each PE traction-motor support bearing 10 has two loadzones, an upper 14 and a lower 16, and these tend to be heaviest around25° from vertical because of commonly-used 25° gear-tooth pressureangle. Both load-contact patterns can be seen in the window half of thePE bearing with the upper load pattern above the lubricatoraccess-window and the lower load pattern below the window. The axiallocation of these contact-patterns is of particular interest, since itis key to understanding the misalignment existing between theaxle-journal and the support bearing. It may be seen in FIG. 1 that theupper load contact-pattern is well centered in the bearing length, whilethe lower load contact-pattern is displaced outwardly, or outboardlytoward the bearing flange. Ideally, both upper and lower loadcontact-patterns should be centered at mid-length of the window, inorder that the wick lubricator, which contacts the journal through thewindow, provides the best possible lubrication. Further, both loadcontact-patterns should be contained within the total axial dimension orlimits of the wick lubricator if at all possible, again to ensure thebest possible lubrication. As may be seen in FIG. 1, only the upper loadzone is centered.

While used prior-art cylindrical-bore bearings have exhibited an upperload-zone 14 that is centered, such is not the case for the lowerload-zone 16, which is skewed toward the outboard end, or bearingflange. Both load zones 14, 16 are actually visible in the window halfof a PE bearing, with the upper load zone above the window and the lowerload zone below the window. The above-described and shown load-patternshave been observed on General Motor's Electric Motor Division (EMD)traction motors, such as that disclosed in above-mentioned U.S. Pat. No.4,940,002, with 8″ diameter axles and standard gauge wheel spacing.

Neither version disclosed in above-mentioned U.S. Pat. No. 4,940,002 iseffective in solving the misalignment of the lower load zone 16. This isso since the bore-profile of U.S. Pat. No. 4,940,002 only takes intoaccount axle-bending torques associated with locomotive weight. However,according to the present invention, it has been discovered that otherloads and torques are present that cause axle-bending and concomitantload-bearing misalignment, which hitherto have not been taken intoaccount into the consideration of a traction-motor support-bearing boreprofile.

SUMMARY OF THE INVENTION

It is a primary objective of the present invention to provide animproved interior contour or profile for a friction support bearing of alocomotive traction motor that more realistically takes into account allbending moments of the truck axle on which the traction motor ispartially mounted, in order to minimize or eliminate misalignmentbetween the support bearing bore and the truck-axle journal, and thusthe misalignment of the upper and lower load zones of the supportbearing. It is also a primary objective of the present invention tomaintain the generally centralized location of the upper load zone of afriction support bearing of a locomotive traction motor exhibited bypresently-used support bearings, while better aligning the lower loadzone thereof to a central, or more central, location.

It is also a primary objective of the present invention to achieve aninterior bore-contour or profile for a friction support bearing of alocomotive traction motor such that such profile may also, under certaincircumstances, be used for the bore of a commutator-end (CE) frictionsupport bearing without adversely affecting the performance of the CEsupport bearing, whereby one, standard, traction-motor friction supportbearing may be used and stocked for either the PE or CE end of thetraction motor support structure

It is also a primary objective of the present invention to achieve aninterior bore-contour or profile for a friction support bearing of alocomotive traction motor such that such profile thereof takes intoaccount torques forces associated with the causing of the bending of thetruck axle that include axle bending due, not only from locomotiveweight, but also those derived from motor tilt through bearingclearances and couple action on the axle deriving from the heavy radialloads on the PE support bearing and the laterally-juxtapositioned axlegear engaged with the pinion gear of the traction motor at the PE endthereof.

According to the present invention, the contour or profile for the boreof a locomotive traction-motor support bearing structure is animprovement over that disclosed in U.S. Pat. No. 4,940,002, and is suchas to preserve the currently-centered loading for the upper load zonebut to move inboardly the lower load zone to a more general centrallocation. The profile of the bore for the support bearing, according tothe invention, takes into account not only truck-axle bending due tolocomotive weight, but also that from motor tilt through bearingclearances, and couple acting on the axle from heavy radial loads on PEsupport bearing and adjacent axle gear. According to the invention, ithas been discovered that the latter two axle-bending factors counteractthe first factor in the upper load-bearing zone, which has accounted forthe generally centrally-located positioning of the upper load zone, asdescribed above. In contrast, however, the latter two axle-bendingfactors combine with the first axle-bending factor to increasemisalignment in the lower load-bearing zone; hence, the observedoutboard-direction misalignment of the lower load-bearing zone describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood with reference to theaccompanying drawings, wherein:

FIG. 1 is an isometric view of a typical, PE window half, used,prior-art, locomotive traction-motor pinion-end support bearing having acylindrical bore and showing the locations of the upper and lowerload-bearing zones thereof;

FIG. 2A is a diagram showing all the additional torques acting in avertical plane on the locomotive truck axle causing bending moments thataffect the location of the upper load zone of a locomotive truckfriction support bearing;

FIG. 2B is a diagram similar to FIG. 2B but showing all the additionaltorques acting in a vertical plane on the locomotive truck axle causingbending moments that affect the location of the lower load zone of alocomotive truck friction support bearing; and

FIG. 3 is a sectional view showing the contour of bore of the supportbearing of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in greater detail, the bore design for thefriction support bearing of the invention is intended, in the preferredembodiment, for use with a locomotive traction-motor manufactured by theElectric Motor Division of General Motors Corporation, as disclosed inabove-discussed U.S. Pat. No. 4,940,002. This traction motor has apinion-end friction support bearing with a bore for passing therethroughthe lubricated axle-journal by which the traction motor is partiallymounted to the truck. The traction motor is also partially supported bythe friction support bearing at the commutator end, and by directmounting to the transoms of the truck through a resilient suspension.This locomotive traction-motor is used with a railway locomotive havingan eight-inch axle and standard gauge wheel-spacing, and approximately60,000-70,000 pounds of axle load, and which has exhibited anapproximately 0.001 inch/inch axle-bending slope at the mid-length ofthe PE support bearing due to locomotive weight alone. As discussedhereinabove, the bore-design of U.S. Pat. No. 4,940,002 only takes intoconsideration the effects on axle-bending from locomotive weight.However, it has been discovered that other factors contribute toaxle-bending which have not been taken into account by the bore-designin this patent. These other factors have been discovered to be thecombined effects of motor tilt and skewing because of bearingclearances, “couple” acting on the axle because of the heavy radialloads on PE support bearing and the adjacent axle-gear thereat, and alsoaxle-bending due to tractive-effort forces and gear-separating forcesacting in the horizontal plain.

Referring now to FIGS. 2A and 2B, misalignment caused by theaxle-bending forces or torque caused by the locomotive weight isindicated by reference symbol M1; misalignment caused by motor tilt andskewing through bearing clearances is indicated by reference symbol M2;that caused by “couple” acting on the axle from heavy radial loads onthe PE support bearing and adjacent axle gear is indicated by referencesymbol M3. Axle-bending caused by tractive-effort forces andgear-separating forces acting in the horizontal plain have, for allintents and purposes, been ignored, however, with only the major factorscausing misalignment in the vertical plane having been considered, whichis the dominant plane of misalignment. The misalignment M1 caused bylocomotive weight derives from the horizontal spacing between the forcesF1 and F2 created by the locomotive weight acting on the journal box 20and the reaction force acting on the wheel 22 from the rail. The secondfactor causing misalignment M2 derives from the simple tilting andskewing of the motor 30 because of bearing clearances.

The third factor causing misalignment M3 caused by couple derives fromthe horizontal spacing between the vertical forces F3 and F4 acting onthe support bearing 24 from the heavy radial loads and thejuxtapositioned driven axle-gear 26 that is driven by the tractionmotor's pinion gear

FIGS. 2A and 2B show the relative deflections and principle loading ofthe locomotive axle in a vertical plane for both forward and reversedirections, and both modes of operation, which are the power mode anddynamic-brake mode, which dynamic-brake mode is accomplished via thetraction motor itself. The sense, or angular direction, of thesecomponents of total misalignment varies with direction of operation andwhether in power mode or dynamic-brake mode of locomotive operation.FIG. 2A shows the factors effecting misalignment in the upper load zone(14 in FIG. 1), while FIG. 2B shows the same for the lower load zone (16in FIG. 1). It is to be understood that the factors causing misalignmentin the power mode in the one direction would be of similar value andsense, or angular direction, as in the dynamic-brake mode in theopposite direction, as indicated in FIGS. 2A and 2B. Thus, the forcevectors shown in FIG. 2A for M2 apply to the power mode in forwardoperation or to the dynamic-brake mode in the reverse direction. Theforce vectors shown in FIG. 2B apply to the power mode in the reverseoperation or to the dynamic-brake mode in the forward direction. Thesame holds true for misalignment contributor M3.

In FIGS. 2A and 2B, the misalignment M1 from locomotive weight has beenassigned a positive, or “+″, sense to the misalignment slope at themidpoint of the PE bearing. Considering the other two dominant factorsof misalignment in the vertical plane, misalignment M2, which is theeffect of motor tilt in bearing clearances, and M3, the effect of couplecreated by adjacent gear and support bearing loads, these have beenassigned either “+” or “−” sense according to whether these componentsadd to, or reduce, the misalignment caused by axle-bending,respectively. Thus, in FIG. 2A, since these factors M2 and M3 counteracttorque M1 for the upper load-zone, and thereby reduce misalignment, theyhave been indicated as negative values. However, in FIG. 2B, sincefactors M2 and M3 add to torque M1 for the lower load-zone 16, andthereby increase misalignment, they have been indicated as positivevalues.

The total misalignment M is the vector sum or combination of the threecomponents, M1 M2 and M3. As discussed hereinabove, examination of upperand lower load-patterns in used bearings has determined that, when thebearing is loaded in its upper load zone (FIG. 2A), the totalmisalignment M is approximately zero, since the load pattern iscentrally located. Thus:M=M 1−M 2−M 3=0,which means that:M 1=M 2+M 3.

For the lower load-zone (FIG. 2B), for total misalignment:M=M 1+M 2+M 3.

From the upper load-zone analysis, it is known that M1=M2+M3, resultingin the conclusion for the lower load zone that:M=2×M 1.

While for simplicity sake, the above analysis has been presented asequations, it is to be understood that these are actually vectorapproximations.

Referring now to FIG. 3, there is shown the bore profile of the supportbearing 30 in accordance with the present invention. In the light of theabove-analysis, the optimum bore-contour for the support bearing in avertical cross-sectional plane is described by a horizontal ornon-sloping line or surface 32 at top, or upper portion, or half, of thebore of the bearing, since examination of used bearings has shown thatthe load zone with such a configuration is already substantiallycentered. It also follows from the analysis described hereinabove thatthe optimum bore-contour for the support bearing in a verticalcross-sectional plane is a sloping line or surface 34 at the bottom, orlower, portion, or half, of the bore, which slope is equal to the totalmisalignment M, which is a correction of 2×M1, as described above. Thesupport bearing 30 is still provided with the flared or conical ends 40,42 as disclosed and discussed in above-discussed U.S. Pat. No.4,940,002. As mentioned above, for an eight-inch truck axle, and alocomotive weight of between 60,000-70,000, M has been determined to beapproximately 0.001 inch/inch. Therefore, in the preferred embodiment,the slope of lower surface 34 would be 0.002 inch/inch.

It is, however, to be understood that the slope of the lower surface 34of the bore 30 may be varied depending upon the type of traction motorthat is to be used, the weight of the locomotive, and the diameter ofthe axle. However, in all cases, the slope of the lower surface will bebased on a combination of the three factors M1, M2 and M3, which factorsmay change owing to these variables of type of traction motor used,locomotive weight, and axle-diameter.

Referring again to FIG. 3, the contour of the mid-section of theinterior bore 30′ of the support bearing 30 may best be described as anon-right, or acute-angle, cone, of which the center section of the bore30′ is the frustroconical section of the cone. This cone is uniquelydefined by an altitude 40 having a slope of 1×M1 to the horizontal, andan apex angle equal to arc tan 2×M1.

While the above-description has been directed to a traction motormanufactured by the EMD of General Motors Corp., the same analysis andbasic bore-configuration of the invention also applies to a tractionmotor made by the General Electric Company. In the case of the GEtraction motor, the application thereof for use in a locomotive of thesame wheel spacing, same approximate range of axle-loads, same generalarrangement of bearings, gears and other parts. The main difference isthat the standard GE axle is 9″ while that for GM is 8″, and that the GEbearing length is approximately three inches shorter, about 9″ for theGE bearing and 12″ for EMD bearing. Axial dimension of the GE wick andwindow is also, therefore, correspondingly shorter. Moreover, in the GEcase, axle-bending M1 would likely be a little less on account of alarger diameter axle. While this GE support bearing has a convex-crownedcentral bore rather than a cylindrical central bore as in the GMversion, the end-relief sections are similar to the GM version. Thisconvex-crowned central bore may be reworked into a cone with concavesides having a skewed axis for using the present invention therewith.

The bore of the support bearing of the present invention may haveapplication in other areas and uses, such as the outer-ring roller pathof rolling-element bearings in the traction-motor environment, and toboth plain and roller bearings in other traction motor applications withvarious axle diameters, axle loading, and wheel gauges, as well as toboth plain and rolling element bearings in other applications, by makingappropriate adjustments for variations in types and additional factorsin the combination of shaft misalignment. These other potentialapplications may include marine and mining equipment, power generationequipment, construction equipment, and other heavy duty, military, andindustrial bearing applications.

While a specific embodiment of the invention have been shown anddescribed, it is to be understood that numerous changes andmodifications may be made therein without departing from the scope andspirit of the invention as set forth in the appended claims.

1. In a locomotive traction-motor support bearing having a bore formounting the traction motor to a truck-axle journal, said bore having anupper surface section and a lower surface section, each said uppersurface section and said lower surface section defining a middle portionthereof; said middle portion of said upper surface section beingsubstantially horizontal, and said middle portion of said lower surfacesection having a downward slope in the outboard direction, wherein theimprovement comprises: said downward slope of said middle portion ofsaid lower surface section having a value based on the values of atleast the lower load-bearing misalignment factors of: locomotive weightM1, motor tilt and skewing M2, and couple-action M3 on the truck-axle.2. The locomotive traction-motor support bearing according to claim 1,wherein said slope is approximately equal to 2×M1.
 3. The locomotivetraction-motor support bearing according to claim 2, wherein said middleportions are defined as the frustroconical section of a cone with analtitude having a slope of substantially 1×M1 to the horizontal, and anapex angle of substantially arc tan 2×M1.
 4. The locomotivetraction-motor support bearing according to claim 1, wherein said middleportions are defined as the frustroconical section of a cone with analtitude having a slope of substantially 1×M1 to the horizontal, and anapex angle of substantially arc tan 2×M1.
 5. The locomotivetraction-motor support bearing according to claim 1, wherein said slopeis approximately equal to 0.002 inch/inch.
 6. The locomotivetraction-motor support bearing according to claim 4, wherein said slopeof said middle portion of said lower surface section is approximatelyequal to 0.002 inch/inch.
 7. In a locomotive traction-motor supportbearing having a bore for mounting the traction motor to a truck-axlejournal, said bore having an upper surface section and a lower surfacesection, each said upper surface section and said lower surface sectiondefining a middle portion thereof; said middle portion of said uppersurface section being substantially horizontal, and said middle portionof said lower surface section having a downward slope in the outboarddirection, wherein the improvement comprises: said downward slope ofsaid middle portion of said lower surface section having a value ofapproximately 2×M1, where M1 is the value of the locomotive-weightmisalignment factor.
 8. The locomotive traction-motor support bearingaccording to claim 7, wherein said middle portions are defined as thefrustroconical section of a cone with an altitude having a slope ofsubstantially 1×M1 to the horizontal, and an apex angle of substantiallyarc tan 2×M1.
 9. The locomotive traction-motor support bearing accordingto claim 7, wherein said downward slope of said middle portion of saidlower surface section is a function of misalignment M, ƒ(M), whereinƒ(M) is at least directly correlated with values of at least two factorsof misalignment, one said factor of misalignment being caused bylocomotive weight, and one said factor of misalignment being caused bycouple-action on the truck-axle.
 10. The locomotive traction-motorsupport bearing according to claim 9, wherein ƒ(M) is also directlycorrelated with the value of an additional factor of misalignment causedby motor tilt and skewing due to bearing clearances.
 11. In a locomotivetraction-motor support bearing having a bore for mounting the tractionmotor to a truck-axle journal, said bore having an upper surface sectionand a lower surface section, each said upper surface section and saidlower surface section defining a middle portion thereof; said middleportion of said upper surface section being substantially horizontal,and said middle portion of said lower surface section having a downwardslope in the outboard direction, wherein the improvement comprises: saiddownward slope of said middle portion of said lower surface section is afunction of misalignment M, ƒ(M), wherein ƒ(M) is at least directlycorrelated with values M1 and M2, where M1 is misalignment caused bylocomotive weight, and M2 is misalignment caused by motor tilt andskewing due to bearing clearances.
 12. The locomotive traction-motorsupport bearing according to claim 11, wherein ƒ(M) is also directlycorrelated with value M3, where M3 is misalignment caused bycouple-action on the truck-axle
 13. The locomotive traction-motorsupport bearing according to claim 11, wherein said slope isapproximately equal to 2×M1.
 14. The locomotive traction-motor supportbearing according to claim 11, wherein said middle portions are definedas the frustroconical section of a cone with an altitude having a slopeof substantially 1×M1 to the horizontal, and an apex angle ofsubstantially arc tan 2×M1.
 15. The locomotive traction-motor supportbearing according to claim 14, wherein said slope is approximately equalto 0.002 inch/inch.
 16. In a support bearing having a bore for receivingan axle element means, said bore having an upper surface section and alower surface section, each said upper surface section and said lowersurface section defining a middle portion thereof, the improvementcomprising: said middle portion of said upper surface section beingsubstantially horizontal, and said middle portion of said lower surfacesection having a downward slope as a function of misalignment M, ƒ(M),wherein ƒ(M) is directly correlated with at least misalignment values M1and M2, where M1 is misalignment caused by load-weight on said axle, andM2 is misalignment caused by motor tilt and skewing due to supportbearing clearances.
 17. The support bearing having a bore for receivingan axle element means according to claim 16, wherein said slope is atleast approximately equal to 2×M1.
 18. The locomotive traction-motorsupport bearing according to claim 16, wherein said middle portions aredefined as the frustroconical section of a cone with an altitude havinga slope of substantially 1×M1 to the horizontal, and an apex angle ofsubstantially arc tan 2×
 19. In a support bearing having a bore forreceiving an axle element means, said bore having an upper surfacesection and a lower surface section, each said upper surface section andsaid lower surface section defining a middle portion thereof, theimprovement comprising: said middle portion of said upper surfacesection being substantially horizontal, and said middle portion of saidlower surface section having a downward slope as a function ofmisalignment M, ƒ(M), wherein ƒ(M) is directly correlated withmisalignment value M1, where M1 is misalignment caused by load-weight onsaid axle; said downward slope of said middle portion of said lowersurface section having a value of approximately 2×M1.
 20. The supportbearing having a bore for receiving an axle element means according toclaim 19, wherein said middle portions are defined as the frustroconicalsection of a cone with an altitude having a slope of approximately 1×M1to the horizontal, and an apex angle of approximately arc tan 2×M1. 21.The support bearing having a bore for receiving an axle element meansaccording to claim 19, in combination with a locomotive traction motor,said support bearing being used in mounting said traction motor to anaxle journal of a locomotive truck; said support bearing being capableof mounting said traction motor to both the pinion end and commutatorend, whereby said support bearing may be used interchangeably either atthe heavily loaded PE position or the lightly loaded CE position withoutadversely bearing performance at said CE position.